Permanent Bubble Arrays from a Cross-Linked Poly(p ara-phenyleneethynylene):  Picoliter Holes without Microfabrication

An azide-substituted poly(para-phenyleneethynylene) (PPE) 4 was prepared by the Heck−Cassar−Sonogashira−Hagihara method. Thin films of 4 form self-assembled bubble arrays from carbon disulfide solution utilizing the breath figure method. The as-formed porous films of 4 are soluble in common solvents, and the air bubbles are interconnected. Upon heating to 300 °C, 4 cross-links and the thin film turn into insoluble matrix with isolated bubbles. The cross-linking process has transformed the bubble arrays of 4 into insoluble picoliter beakers or picoliter vials, whose diameters are approximately 3.0 and 1.5 μm at the top and bottom, respectively.